1. Field of the Invention
The present invention relates to a glue unit having a glue shoe with an adjustable metering plate and a glue wheel. The glue unit is for use in applying glue or the like to a glue flap of a paperboard box blank in a folder-gluer machine.
2. Brief Description of the Prior Art
In the manufacture of a cardboard or paperboard shipping container, glue is applied to a tab called a glue flap that projects from one of the outside panels of a box blank. After the glue is applied, the two outside panels are folded onto the two inside panels to convert the box bank into a collapsed flat folded form. This operation is performed in a folder-gluer machine. The flat folded blank may thereafter be shipped to a customer for erection and filling with product to be shipped therein.
The glue is usually applied to the glue flap so that, when the box is erected for filling the glue flap is on the inside of the box. The filling of some containers, however, requires that the glue flap be on the outside of the container, even though aesthetically, the glue flap is preferably on the inside. Since the box blank may be folded with the glue flap either above or below the adjacent panel, it is necessary for the gluer to be able to apply the glue either above and below the flap.
In the past, applicator wheels and shoes have been used to apply glue to the glue flap. With these devices, excessive wear takes place if the fit between the shoe and the wheel is too snug but if the shoe is too loose, glue may be slung off the wheel. There have also been problems in applying the glue uniformly from a position above and below the flap.
Extruders have been used in place of prior art applicator wheels and shoes because of the above-mentioned problems. To create a strong container, however, the glue must be applied to the glue flap uniformly and in an effective amount. When an extruder is used, it must be turned on and off quickly between successive glue flaps. As the box blanks travel through the gluer-folder, it is difficult, if not impossible, to obtain a uniform bead of glue consistently over the entire length of each glue flap. Another problem is that extruders drip glue from the nozzle and the nozzle tends to clog up with dried glue changing the amount of glue applied. When the flaps are not glued adequately, the container may rupture while it is being filled or during shipment of the product. Sometimes the extruders overspray the box blanks so that the flat folded blanks stick together. These problems tend to be reported by the customer and get back to the maker of the container.
Glue shoes and wheels are easier to control than extruders and would be preferred if the disadvantages of the prior art could be overcome.